Field of the Invention
The present invention relates to a pigment dispersion and to a toner that contains this pigment dispersion.
Description of the Related Art
Pigments, which generally have small particle diameters, tend to present strong cohesive forces among the pigment particles and as a consequence their dispersion in mediums such as organic solvents and molten resins can easily become unsatisfactory. The tinting strength of a pigment ends up declining when the pigment exhibits an unsatisfactory dispersibility.
The pigment particles must be highly dispersed in order to obtain a high clarity in the case of offset inks, gravure inks, paints and coatings, inkjet inks, inks for color filters, and so forth. Similarly, a high pigment dispersibility is also required for toners in order to obtain a high clarity. The use of a pigment in combination with a dispersing agent for dispersing the pigment has therefore been proposed in order to increase pigment dispersibility. In particular, various dispersing agents have been proposed for the individual colored toners, e.g., yellow, magenta, cyan, and black, in order to increase pigment dispersibility in a toner particle.
Specifically, the use of an azo skeleton structure-containing compound as a dispersing agent in order to improve the dispersibility of the azo pigments in yellow toners is disclosed in Japanese Patent Application Laid-open No. 2012-067285. The use of a special polyester-type dispersing agent in order to improve the dispersibility of the magenta pigments in magenta toners is disclosed in Japanese Patent Application Laid-open No. 2006-030760. The use as a dispersing agent of a polymer that contains sodium styrenesulfonate as a monomer unit in order to improve the dispersibility of the phthalocyanine pigments in cyan toners is disclosed in Japanese Patent Application Laid-open No. H03-113462. The use as a dispersing agent of a copolymer comprising a styrenic monomer and an acrylate ester (or methacrylate ester) monomer in order to improve the dispersibility of the carbon black in black toners is disclosed in Japanese Patent Application Laid-open No. H06-148927.